1. Field of the Invention
The invention relates to well-drilling techniques, and more particularly it relates to downhole thermoacoustic devices.
The invention is intended for utilization in the oil and gas industry, for exerting thermoacoustic action upon the hole-bottom zone of oil and gas wells so as to intensify the rate of development and production in fields with viscous paraffin-containing oils, as well as in fields containing considerable quantities of dissolved salts tending to leave deposits affecting the oil and gas permeability of the hole-bottom area of a well in the course of developing the latter.
2. Description of the Prior Art
The application of the method of thermoacoustic action upon the hole-bottom zone of wells is based on the phenomena of thermodynamic interaction of heat and sound fields in crude oil and natural gas reservoir formations. The phenomena significantly increase the effective heat conductivity of oil and gas reservoirs, and, hence, expand the area of heat action upon the hole-bottom zone of a well. Following the conduction thermoacoustic action upon the hole-bottom zone of a well, there is observed restoration of the oil and gas permeability of the reservoir, affected previously either by deposits of field paraffin and salts, or by ingress of clay into the hole-bottom zone.
There is known a downhole thermoacoustic device (see "Investigation of heat action by deep-hole electric heaters" by E. M. Simkin--a dissertation for Candidate of Technical Sciences degree, 1968, Collections of All-Union Scientific Research Institute of the Ministry of Oil Industry of the USSR), intended for exerting electric heat action upon the hole-bottom zone of an oil or gas well and comprising a heater with a terminal chamber rigidly linked with a radiator or source of acoustic oscillation, including two electromagnets mounted on a common shaft internally of a cylindrical housing. The top electomagnet of the acoustic oscillation radiator is stationary, while the bottom one is movable jointly with the heater along the common shaft. With an electric current flowing, the electromagnets are periodically attracted, although the top electromagnet remains stationary, while the bottom electromagnet and the heater are reciprocated. In this manner there are generated adjustable longitudinal acoustic oscillations of the electric heater in the well, which expands the heated zone.
However, this downhole thermoacoustic device generates oscillation of low intensity which propagate predominantly longitudinally of the borehole, on account of the longitudinal reciprocation of the bottom electromagnet with the heater, whereas the direction of propagation of the oscillation is preferably substantially normal to the axis of the borehole, so as to exert effective thermoacoustic action upon the hole-bottom area.
The known device generates low-frequency oscillation (up to 100 Hz) which fails to create the thermoacoustic effect which is of the threshold character and would take place at a certain range of frequencies.
The device would not enable focusing of the heat field, being devoid of elements capable of controlling the heat variables of the thermoacoustic field.
On account of the incorporation of movable parts and the eventuality of the fluid-tightness of the deivce becoming affected in operation, the performance reliability of the device is inadequate.
With the inter-hole hydraulic static pressure increasing as the device is run down the hole to a predetermined depth, the acoustic parameters of the device are affected by the damping action of the hole fluid.
On account of the longitudinal oscillation of the hole fluid column, some heat is carried upwardly, which affects the temperature conditions of the performance of the electric cable supplying the device and would not enable to exert efficient heat action upon the hole-bottom zone of the well.
Thus, the above described thermoacoustic device for the above discussed reasons would not enable creation of a thermoacoustic field with a high intensity of the acoustic radiation propagating in the radial direction.